TYPES OF PATTERN
The types of the pattern and the description of each are given as under.1. One piece or solid pattern
2. Two piece or split pattern
3. Cope and drag pattern
4. Three-piece or multi- piece pattern
5. Loose piece pattern
6. Match plate pattern
7. Follow board pattern
8. Gated pattern
9. Sweep pattern
10. Skeleton pattern
11. Segmental or part pattern
1. Single-piece or solid pattern
Solid pattern is made of single piece
without joints, partings lines or loose pieces. It is the
simplest form of the pattern. Typical single piece
pattern is shown
in Fig. |
| Single-piece or solid pattern |
2. Two-piece or split pattern
When solid pattern is difficult
for withdrawal from the mold cavity, then solid pattern is splited
in two parts. Split pattern
is made in two pieces which are joined at the parting line by means of dowel
pins. The splitting at
the parting line is done to
facilitate the withdrawal of the pattern. A typical example is shown in Fig. |
| Two-piece or split pattern |
3. Cope and
drag pattern
In this case, cope and drag part of the mould
are prepared separately. This is done when the complete mould is too heavy to
be handled by one operator. The pattern is made up of two halves, which are
mounted on different plates. A typical example of match plate pattern is shown
in Fig. |
| Cope and drag pattern |
4. Three-piece or multi-piece
pattern
Some patterns are of complicated kind in shape
and hence can not be made in one or two pieces because of difficulty in
withdrawing the pattern. Therefore these patterns are made in either three
pieces or in multi-pieces. Multi molding flasks are needed to make mold from
these patterns.5. Loose-piece Pattern
Loose piece pattern is used
when pattern is difficult for withdrawl from the mould. Loose pieces are provided on the pattern
and they are the part of pattern. The main pattern
is removed first
leaving the loose
piece portion of the pattern in the mould. Finally the loose piece is withdrawal
separately leaving the intricate
mould. |
| Loose piece pattern |
6. Match plate pattern
This
pattern is made in two halves and is on mounted on the opposite sides of a
wooden or metallic plate, known as match plate. The gates and runners are also
attached to the plate. This pattern
is used in machine molding. A
typical example of match plate pattern is shown in Fig. |
| Loose piece pattern |
7. Follow board pattern
When the use of solid
or split patterns becomes difficult,
a contour corresponding to the exact shape of one half of the pattern is
made in a wooden board, which is called a follow board and it acts as a molding
board for the first molding
operation as shown in fig. |
Follow board pattern |
8. Gated pattern
In the mass production of casings, multi
cavity moulds are used. Such moulds are formed by joining a number of patterns
and gates and providing a common runner for the molten metal, as shown in Fig. These patterns are made of metals, and metallic pieces to form gates and
runners are attached to the pattern. |
Gated pattern |
9.
Sweep pattern
Sweep patterns are used for forming large
circular moulds of symmetric kind by revolving a sweep attached to a spindle as
shown in Fig. Actually a sweep is a template of wood or metal and is
attached to the spindle at one edge and the other edge has a contour depending
upon the desired shape of the mould. The pivot end is attached to a stake of
metal in the center of the mould. |
| Sweep patterns |
10. Skeleton pattern
When only a small number of large and heavy
castings are to be made, it is not economical to make a solid pattern. In such cases, however, a skeleton pattern
may be used. This is a ribbed
construction of wood which forms an outline of the pattern to be made.
This frame work is filled with loam sand and rammed. The surplus
sand is removed by strickle board. For round shapes,
the pattern is made in two halves which are joined with glue or by means of
screws etc. A typical skeleton
pattern is shown in Fig. |
Skeleton pattern |
11. Segmental pattern
Patterns of this type are generally used for
circular castings, for example wheel rim, gear blank etc. Such patterns are sections
of a pattern so arranged as to form a complete mould by being moved to
form each section of the mould. The movement of segmental pattern is guided by the use of a central pivot. A segment pattern for a
wheel rim is shown in Fig. |
| Segmental pattern |